An image displayed on a screen of an information processor can be copied by taking a screen shot. That is, data of the image displayed on the screen can be obtained by capturing display data stored in the display memory.
In an attempt to prevent such fraudulent acts, Patent Literature 1 below discloses a technology for randomly selecting S for each pixel of an original image, generating a first converted image obtained by adding S to each pixel value and a second converted image obtained by subtracting S from each pixel value, and displaying these two converted images while switching them at a high speed. In accordance with this technology, even though a viewer recognizes as if the original image is displayed, it is possible to prevent fraudulent acquisition of original image data because the data obtained by a screen shot is the first or the second converted image.